The power and usefulness of today's digital integrated circuit (IC) devices is largely attributed to the increasing levels of integration. More and more components (resistors, diodes, transistors, and the like) are continually being integrated into the underlying chip, or Integrated Circuit (IC). The starting material for typical ICs is high purity silicon. The material is grown as a single crystal and takes the shape of a solid cylinder. This crystal is then sawed (like a slice of bread) to produce wafers typically 10 to 30 cm in diameter and 250 microns thick.
The geometry of the features of the IC components are commonly defined photographically through a process known as photolithography. Very fine surface geometry can be accurately reproduced by this technique. The photolithography process is used to define component regions and build up components one layer on top of another. Complex ICs can often have many different built up layers, each layer having components, each layer having differing interconnections, and each layer stacked on top of the previous layer. The resulting topography of these complex IC's often resemble familiar terrestrial “mountain ranges,” with many “hills” and “valleys” as the IC components are built up on the underlying surface of the silicon wafer.
Submicron devices, e.g. transistors smaller than 1 micron in size, are formed in the various layers that form the IC. Thousands or millions of the submicron devices can be utilized in a typical IC. However, circuits are continually becoming more complex and more capable. Hence, there is a constant need for increasing the number of components that are included on an IC. However, the size of an IC is frequently limited to a given die size on a wafer. Consequently, a constant need arises to reduce the size of devices in an IC.
As device size shrinks, the electrical Resistance-Capacitance (RC) delays and crosstalk associated with backend metallization become more significant. At some point, a threshold between the size of the device and the amount of interference it can sustain, is crossed. After this threshold, the operation of the device is compromised. Hence, a need arises to reduce the RC sensitivity of a deep submicron device.
One conventional method that reduces RC sensitivity of a device and an IC, uses low dielectric constant materials, k, for deep submicron devices. However, low dielectric materials have material properties that are incompatible with subsequent materials deposited thereon. Additionally, the low dielectric materials have material properties that are detrimental in the Chemical Mechanical Polishing (CMP) process. Resultantly, a need arises for modifying the low dielectric material to make it more compatible with subsequent material layers and with CMP processes.
Referring now to prior art FIG. 1, a wafer with a conventional porous material layer interfaced with a conventional cap layer is shown as a side view of. Wafer 100 includes a substrate 102, a porous material 104, and a cap layer 106. Porous material 104 is deposited on top of substrate 102. And cap material is deposited on top of porous material 104. Porous material 104 is used because it has a low dielectric constant. However, a low dielectric material typically has low mechanical strength. Additionally, the porous material becomes impregnated with the CMP slurry during polishing. The slurry impregnated in porous material 104 causes other problems such as out gassing in subsequent high temperature processes and a high dielectric constant which hampers its operational ability. Thus, a cap layer, e.g. cap layer 106, is required on top of porous material 104 to make it at least marginally compatible with subsequent semiconductor fabrication operations, such as CMP. Consequently, cap layer 106 is deposited on top of porous material 104. Thus, cap layer 106 is used as a sacrificial layer for CMP planarization of the metal topography.
Besides these drawbacks, conventional porous layer 104, of prior art FIG. 1, has a top surface that is significantly rough, as indicated by peaks 108b. Because of the porosity and the rough and irregular top surface of porous layer 104, cap layer 106 has very poor adhesion to porous layer 104. Consequently, a need arises for a method and an apparatus that provides a smoother and less porous surface for the porous layer so as to improve the adhesion between the porous layer and the cap layer.
Because of the poor adhesion, cap layer 106 frequently delaminates during the CMP operation. Delamination of cap layer 106 from porous layer 104 occurs in damascene processing as well as during copper and aluminum CMP processing. Consequently, a need arises for a resilient interface between the porous layer and the cap layer such that CMP operations can be performed without delamination.
In summary, a constant need arises to reduce the size of devices in an IC and to reduce the RC sensitivity of a deep submicron device. Additionally, a need arises for modifying the low dielectric material to make it more compatible with subsequent material layers and with CMP processes. Furthermore, a need arises for a method and an apparatus that provides a smoother and less porous surface for the porous layer so as to improve the adhesion between the porous layer and the cap layer. Yet another need arises for a resilient interface between the porous layer and the cap layer such that CMP operations can be performed without delamination.